Nickel recovery

ABSTRACT

The nickel content of nickel-magnesium alloy fines containing up to 50 percent silicon is recovered in usable metal form by reacting said fines exothermically with powdered iron oxide, an alkali metal nitrate and magnesia fluxing ingredients to provide a nickel-containing metal phase and a fluid magnesia-containing slag phase.

United States Patent [151 3,647,419

Pargeter et al. 1 Mar. 7, 1972 [54] NICKEL RECOVERY 2,610,911 9/1952 Udy ..75/27 X [72] inventors: John K Puget", Warwick NY'; Loris 2,222,233 Schott ..75/82 M. Diran, Montclair, NJ. l

[ 1 g The International Nickel p y 2,485,760 10/1949 Millisetal. ..75/130 x New York, NY. 22 Filed; 31 19 9 Primary Examiner-Henry w. Tarring, ll [21] A l N 889 726 AttorneyMaurice L. Pinel [57] ABSTRACT [52] US. Cl ..75/82, 75/27, 75/130 The nickel content of nickel magnesium alloy fines containing 2; Czzb 7/00 02% up to 50 percent silicon is recovered in usable metal form by le 0 are ..75/82,2 reacting said fines exothermicany with powdered iron oxide an alkali metal nitrate and magnesia fluxing ingredients to pro- [56] References cued vide a nickel-containing metal phase and a fluid magnesia- UNITED STATES PATENTS cOntnining slag p Goldschrnidt ..75/27 X 5 Claims, No Drawings NICKEL RECOVERY The use of nickel-magnesium-silicon alloys for the purpose of introducing magnesium into molten cast iron so as to produce magnesium-containing cast iron (ductile iron) has been common practice for a considerable period of time. One such alloy for this purpose is described in US. Pat. No. 2,563,859 and comprises an alloy which may contain about 12 percent to about 20 percent magnesium, about 30 percent to about 50 percent silicon, up to about 12 percent iron and the balance essential nickel. Usually, nickel comprises about 40 percent or more of the alloy. in preparing the alloy, it has been usual practice to first melt down nickel with the required amount of silicon added either as silicon metal or as ferrosilicon (for example, an alloy containing about 75 percent or more silicon with the remainder iron), introducing magnesium as magnesium metal billets or sticks into the resulting bath and, after dissolution of magnesium into the bath, casting the melt into a cake. The resulting solidified cake is then crushed to provide alloy in the size ranges desired by the foundry. in the crushing operation a proportion of fine material which is unsuitable for use as an addition agent is produced. It has been found that the physical and chemical nature of this fine material is such that it is impractical to melt the fine material as a charge, per se, in any of the regular melting furnaces readily available to a foundry. Accordingly, the production of such fines has been a source of economic loss to the manufacturer of nickel-magnesium-silicon alloy. In the course of preparing nickel-magnesium-silicon alloy in any considerable quantity a substantial proportion of fines is accumulated over a period of time. Since the fine materials contain a substantial proportion of nickel, i.e., approximately 40 percent or more nickel, it is important that a means be provided whereby the nickel content of the fines can be recovered in usable form. It is to the solution of this problem that the present invention is directed.

It is an object of the present invention to provide a simple and effective means for recovering in usable form the nickel content of fine alloyed materials comprising nickel, magnesium, and silicon.

Generally speaking, the present invention is directed to a method for recovering nickel from fine alloyed material, i.e., materials having a particle size not greater than about onequarter inch and containing about percent to about 25 percent magnesium, up to about 50 percent silicon, e.g., about 25 percent to about 35 percent silicon, up to about 12 percent iron and the balance essentially nickel, e.g., at least about 40 percent nickel. In accordance with the invention the aforementioned fine materials are mixed with proportioned amounts of powdered iron oxide, e.g., magnetite (Fe O hematite Fe,o, or mill scale, an alkali metal nitrate, silica and fluorspar. The mixture is charged into a refractory container and ignited. The mixture reacts exothermically, principally by oxidation of the magnesium content in the fine materials, and produces a melt comprising a magnesia-containing slag and metal. The metal contains a major proportion of the nickel and a substantial proportion of the silicon contained in the fine material while the slag contains substantially all of magnesium (as MgO) and a proportion of the silicon (as SiO contained in the initial fine materials. The function of the sand and fluorspar additions in the original mixture is to form a slag which is fluid at the temperature generated so that ready separation of metal and slag is accomplished. The powdered ingredients of the mix have particle sizes not exceeding about 8 mesh, e.g., about 100 mesh to about 8 mesh, as referred to the Tyler Standard Screen (TSS) mesh size.

it is important that the proportioning of iron oxide, e.g., magnetite, hematite, etc., to magnesium contained in the fine materials should be such that the iron oxide exceeds in weight the amount of magnesium in the fines. It is also important that the alkali metal nitrate present in the charge exceed in weight the magnesium content of the fines. For example, the weight ratio of iron oxide to magnesium in the fines should be at least about l.25: l and the weight ratio of alkali metal nitrate to magnesium in the fines should be at least l.4:l. The proportion of silica in the charge is also related to the proportion of magnesium in the fines being treated. Generally it is found that about 4 percent to about 8 percent of silica in the charge, based upon a magnesium content in the fines of about 15 percent, is sufficient. The fluorspar content of the charge can be quite small, e.g., on the order of up to about two percent by weight of the charge. Up to about 50 percent by weight of iron oxide in the charge can be replaced by nickel oxide (M0) on an equivalent oxygen content basis. When this variation is employed, substantially all the nickel in the nickel oxide addition to the charge is recovered in the metal phase when the exothermic reaction is complete.

it is to be appreciated that the exothermic reaction proceeds very rapidly throughout the charge once the reaction has been initiated. Magnesium in the fine material is converted very rapidly to magnesia with evolution of copious quantities of heat. Since a portion of silicon in the fines is also oxidized, some silica will result from this reaction. The amount of silica thus formed is generally insufficient to form a fluid slag with the magnesia generated by the reaction. it is to be appreciated in this connection that magnesia is a very high melting point refractory material and it is necessary to provide sufficient silica in the initial charge to insure the formation of a fluid slag with the magnesia generated. The fluorspar addition in the charge is also helpful in this connection. It is further to be appreciated that a portion of the iron content of the iron oxide in the initial charge will be reduced to iron metal which will report with the molten metal portion of the reaction mixture. However, a portion of the original iron oxide will remain in the slag as iron oxide (FeO). it is desirable that the molar ratio of magnesia to silica plus FeO in the resultant slag not exceed about 1.3:1, i.e., be approximately 1:1 in order to assure that a fluid slag will form. It is found that the alkali metal oxide, e.g., sodium oxide or potassium oxide, resulting from decomposition of the alkali metal nitrate also acts to improve the fluidity of the slag formed. For this reason, the alkali metal nitrates are employed rather than ammonium nitrate.

In order to give those skilled in the art a better appreciation of the advantages of the invention the following examples are given.

EXAMPLE 1 Three ten kilogram charges were prepared comprising about 6.5 kilograms of nickel-magnesium-silicon alloy fines having a maximum particle size of about 8 mesh and containing about 45 percent nickel, about 31 percent silicon and about 14 percent magnesium, mixed with 1.5 kilograms of powdered magnetite (50 mesh) and 1.3 kilograms of sodium nitrate crystals. Five percent by weight of the total charge comprised sand (silica) having a particle size of abut 60 mesh and about two percent by weight of the total charge comprised powdered fluorspar mesh). Each charge was placed in a brick-lined vessel and ignited by means of an aluminum-sodium nitrate fuse. The reaction took place very rapidly to form metal and slag which separated to form a metal button" with an overlying slag layer. The metal buttons from the three runs were analyzed for nickel, silicon, iron and magnesium with the following results.

TABLE 1 Metal NI Alloy Ni Si Fe Mg Weight yield No. I: X: Grams l S] 26.6 20.! 0.43 5150 87 2 51.6 26.4 l8.7 0.21 4950 84 The slag from Alloy No. 2 was analyzed and was found to contain, by weight, 2.7 percent nickel, 18 percent silicon, 8 percent iron and 25 percent magnesium. From the foregoing, it is to be seen that the nickel content of the alloy fines was converted to a nickel-silicon-iron alloy with a high yield of nickel contained in the original fines, with low loss of nickel to the slag. It is found that the nickel-containing metal produced is readily converted again to a magnesium-containing addition alloy merely by melting the nickel-containing metal and adding further magnesium to the melt.

EXAMPLE" A 1,100 kilogram charge was prepared which contained 650 kilograms of alloy fines containing about 45 percent nickel, about 30 percent silicon and about percent magnesium. The fines were mixed with 140 kilograms of magnetite having a particle size of about mesh, about 130 kilograms of sodium nitrate having a particle size of about 20 mesh with five weight percent of silica sand having a maximum particle size of about 40 mesh and about two weight percent of fluorspar having a particle size of about 200 mesh. The mixture was ignited in a brick-lined container and reacted exothermically to produce nickel-containing metal and a magnesia slag. The entire metal remained in the molten state for about 180 minutes thereby assuring good metal-slag separation. Upon cooling, the metal ingot was readily separated from the slag with a sharply defined demarcation between the metal and slag phases. A nickel recovery in the metal phase of 99 percent was achieved.

It is found that if the iron oxide addition is insufficient in weight proportion to the magnesium content of the fines being treated that the nickel content in the metal phase is sharply reduced and that a deficiency in iron oxide content of the charge can not be compensated for by increasing the proportion of sodium nitrate.

It is found, however, that a proportion of the required iron oxide can be replaced by nickel oxide as is shown by the following example.

EXAMPLE III A charge comprising six kilograms of fines having the composition of Example I, about one kilogram of a nickel oxide in the form of high temperature nickel oxide granules produced by fluid bed roasting nickel sulfide at a temperature above the fusion point of nickel sulfide, about one kilogram of magnetite, about l.2 kilograms of sodium nitrate, about three weight percent of silica sand and about one weight percent of fluorspar was prepared and ignited in a brick-lined vessel. The maximum particle size of the ingredients in the charge was 8 mesh TSS. Excellent slag-metal separation was obtained as a result of the reaction and a nickel-silicon-iron alloy ingot weighing about five kilograms and containing 58.6 percent nickel with a nickel yield of 82 percent was obtained.

The present invention affords an extremely expeditious way to recover nickel from nickel-magnesium-silicon alloy fines. High recoveries of nickel result and a useful product is yielded directly. Thus, the nickel-containing ingot which results is readily melted in conventional equipment including arc furnaces, induction furnaces, and the like, without encountering the problems which made the initial nickel-containing fine material almost impossible to treat in such conventional furnaces.

While the invention has been illustrated in connection with the recovery of nickel from fines resulting from the crushing of nickel-magnesium-silicon alloys, it is to be understood that the invention is equally applicable to the recovery of nickel from the fines resulting from the crushing of nickel-magnesium alloys of the kind known in the art as magnesium additives for the production of ductile iron. Thus, nickel-magnesium alloy fines containing about l0 percent to about 25 percent magnesium, up to four percent carbon and the balance essentially nickel may be employed. Such alloys are disclosed, for example, in U.S. Pat. No. 2,529,346, particularly alloys containing about 10 percent to about 20 magnesium, about 1.25 percent to about four percent carbon and the balance essentially nickel. it is to be understood that such alloys and nickelmagnesium-sihcon alloys are included in the term nickelmagnesium alloys as used herein and in the appended claims.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. The method for recovering nickel from nickel-magnesium alloy fines containing about 10 percent to about 25 percent magnesium and up to about 50 percent silicon which comprises mixing said fines with powdered iron oxide, an alkali metal nitrate, magnesium-fluxing amounts of silica and fluorspar, with the weight ratios of iron oxide and of alkali metal nitrate to the magnesium content of the fines in the mixture each exceeding unity, and then igniting said mixture to melt the constituents thereof and produce a nickel-containing metal melt and a fluid magnesia-containing slag wherein the molar ratio of magnesia to silica plus FeO does not exceed about 1.3:1 whereby high recovery of nickel from the fines is achieved in the metal melt and whereby good metal-slag separation is obtained.

2. The method according to claim 1 wherein the weight proportion of silica in the charge is about four percent to about eight percent when the magnesium content of the tines is about l5 percent.

3. The method according to claim 1 wherein the mixture additionally contains nickel oxide.

4. The method according to claim 1 wherein the alloy fines contain at least about 40 percent nickel.

5. The method according to claim 4 wherein the alloy fines contain about 25 percent to about 50 percent silicon. 

2. The method according to claim 1 wherein the weight proportion of silica in the charge is about four percent to about eight percent when the magnesium content of the fines is about 15 percent.
 3. The method according to claim 1 wherein the mixture additionally contains nickel oxide.
 4. The method according to claim 1 wherein the alloy fines contain at least about 40 percent nickel.
 5. The method according to claim 4 wherein the alloy fines contain about 25 percent to about 50 percent silicon. 